83 lines
2.3 KiB
C++
83 lines
2.3 KiB
C++
#include <map>
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#include <cstring>
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#include <fstream>
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#include <sstream>
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#include <iostream>
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/* This is just a very simple and inefficient demo of async responses,
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* please do roll your own variant or use a database or Node.js's async
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* features instead of this really bad demo */
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struct AsyncFileReader {
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private:
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/* The cache we have in memory for this file */
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std::string cache;
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int cacheOffset = 0;
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/* The pending async file read (yes we only support one pending read) */
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std::function<void(std::string_view)> pendingReadCb;
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int fileSize;
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std::ifstream fin;
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uWS::Loop *loop;
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public:
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/* Construct a demo async. file reader for fileName */
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AsyncFileReader(std::string fileName) {
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fin.open(fileName, std::ios::binary);
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// get fileSize
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fin.seekg(0, fin.end);
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fileSize = fin.tellg();
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//std::cout << "File size is: " << fileSize << std::endl;
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// cache up 1 mb!
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cache.resize(1024 * 1024);
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//std::cout << "Caching 1 MB at offset = " << 0 << std::endl;
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fin.seekg(0, fin.beg);
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fin.read(cache.data(), cache.length());
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cacheOffset = 0;
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// get loop for thread
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loop = uWS::Loop::defaultLoop();
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}
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/* Returns any data already cached for this offset */
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std::string_view peek(int offset) {
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/* Did we hit the cache? */
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if (offset >= cacheOffset && ((offset - cacheOffset) < cache.length())) {
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/* Cache hit */
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//std::cout << "Cache hit!" << std::endl;
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return std::string_view(cache.data() + offset - cacheOffset, cache.length() - offset + cacheOffset);
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} else {
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/* Cache miss */
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//std::cout << "Cache miss!" << std::endl;
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return std::string_view(nullptr, 0);
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}
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}
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/* Asynchronously request more data at offset */
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void request(int offset, std::function<void(std::string_view)> cb) {
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// std::async this
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//std::cout << "Caching 1 MB at offset = " << offset << std::endl;
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fin.seekg(offset, fin.beg);
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fin.read(cache.data(), cache.length());
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cacheOffset = offset;
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// Loop.defer this
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cb(std::string_view(cache.data(), cache.length()));
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}
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/* Abort any pending async. request */
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void abort() {
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}
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int getFileSize() {
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return fileSize;
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}
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};
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